The project sponsor set forth a number of requirements including that the cartridge fit in the M4 carbine and be capable of firing heavy-for-caliber projectiles at subsonic velocity using suppressors.

The .45 Professional was ruled out because, in an interview with industry press, the developer of said cartridge stated that steel proprietary to General Motors was used in the bolts and extractor to withstand the high operating pressures.

Research had indicated that a short belted cartridge called the .458 × 1.5" Barnes had been adopted for use in suppressed bolt-action rifles for use in South East Asia during the Vietnam War.

It was shown as effective in terms of ballistics, firing a 500-grain bullet subsonically, but not ideally suited for its role due to the size and weight of the platform.

The initial prototype brass still bore the .50 AE head stamp and this has caused some confusion, as the SOCOM case is longer with a narrower rim.